使用OkHttp，设备切换路由后，访问网络出现长时间无响应，很久以后才抛出UnknownHostException，这明显不是我们想要的，我们设置的connectTimeout属性似乎对dns的解析不起作用。

我们先看看OkHttpClient有没有关于Dns的相关设置，发现OkHttpClient的Builder类存在dns()方法可以设置一个Dns类型参数。
Dns类源码如下：

package okhttp3;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.List;
 * A domain name service that resolves IP addresses for host names. Most applications will use the
 * {@linkplain #SYSTEM system DNS service}, which is the default. Some applications may provide
 * their own implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4
 * addresses, or to force a specific known IP address.
 * <p>Implementations of this interface must be safe for concurrent use.
public interface Dns {
   * A DNS that uses {@link InetAddress#getAllByName} to ask the underlying operating system to
   * lookup IP addresses. Most custom {@link Dns} implementations should delegate to this instance.
  Dns SYSTEM = new Dns() {
    @Override public List<InetAddress> lookup(String hostname) throws UnknownHostException {
      if (hostname == null) throw new UnknownHostException("hostname == null");
      try {
        return Arrays.asList(InetAddress.getAllByName(hostname));
      } catch (NullPointerException e) {
        UnknownHostException unknownHostException =
            new UnknownHostException("Broken system behaviour for dns lookup of " + hostname);
        unknownHostException.initCause(e);
        throw unknownHostException;
   * Returns the IP addresses of {@code hostname}, in the order they will be attempted by OkHttp. If
   * a connection to an address fails, OkHttp will retry the connection with the next address until
   * either a connection is made, the set of IP addresses is exhausted, or a limit is exceeded.
  List<InetAddress> lookup(String hostname) throws UnknownHostException;
这是一个抽象类，并且其中已经写好了默认实现并赋值给了SYSTEM对象。
 透过代码我们可以看出，解析dns主要是靠这行代码：
 
InetAddress.getAllByName(hostname)
Ok，我们已经知道如何解析dns并设置给OkHttpClient了，现在我们只需要重新实现这个过程，插入超时控制，并让OKHttp调用新的Dns解析就好了。
 
实现抽象类Dns
 
package com.x.http;
import okhttp3.Dns;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
public class XDns implements Dns {
    private long timeout;
    public XDns(long timeout) {
        this.timeout = timeout;
    @Override
    public List<InetAddress> lookup(final String hostname) throws UnknownHostException {
        if (hostname == null) {
            throw new UnknownHostException("hostname == null");
        } else {
            try {
                FutureTask<List<InetAddress>> task = new FutureTask<>(
                        new Callable<List<InetAddress>>() {
                            @Override
                            public List<InetAddress> call() throws Exception {
                                return Arrays.asList(InetAddress.getAllByName(hostname));
                new Thread(task).start();
                return task.get(timeout, TimeUnit.MILLISECONDS);
            } catch (Exception var4) {
                UnknownHostException unknownHostException =
                        new UnknownHostException("Broken system behaviour for dns lookup of " + hostname);
                unknownHostException.initCause(var4);
                throw unknownHostException;
 上面的实现主要依赖了FutureTask可以设置任务执行时间的特性，不明白的同学可以自行学习一下。
 然后把新的dns解析类设置给OkHttpClient
 
    public static OkHttpClient createClient(long timeout, long writeTimeout,
     long readTimeout, boolean bRetry) {
        OkHttpClient.Builder builder = new OkHttpClient.Builder()
                .connectTimeout(timeout, TimeUnit.MILLISECONDS)
                .dns(new XDns(timeout))
                .retryOnConnectionFailure(bRetry);
        if (writeTimeout > 0)
            builder.writeTimeout(writeTimeout, TimeUnit.MILLISECONDS);
        if (readTimeout > 0)
            builder.readTimeout(readTimeout, TimeUnit.MILLISECONDS);
        OkHttpClient client = builder.build();
        client.dispatcher().setMaxRequestsPerHost(10);
        client.dispatcher().setMaxRequests(30);
        return client;
转载于：https://blog.csdn.net/quwei3930921/article/details/85336552#commentBox 感谢作者的辛苦付出
                    问题使用OkHttp，设备切换路由后，访问网络出现长时间无响应，很久以后才抛出UnknownHostException，这明显不是我们想要的，我们设置的connectTimeout属性似乎对dns的解析不起作用。如何解决我们先看看OkHttpClient有没有关于Dns的相关设置，发现OkHttpClient的Builder类存在dns()方法可以设置一个Dns类型参数。Dns类...
OkHttpClient client = new OkHttpClient.Builder()
                    .connectTimeout(5, TimeUnit.SECONDS)
                    .readTimeout(5, TimeUnit.SECONDS)
				
Android OkHttp是一个开源的HTTP客户端库，可以用来发送HTTP请求和获取数据。使用OkHttp获取数据的步骤如下：
1. 添加OkHttp依赖库到项目中。
2. 创建OkHttpClient对象，用于发送HTTP请求。
3. 创建Request对象，设置请求的URL、请求方法、请求头等信息。
4. 调用OkHttpClient的newCall方法，传入Request对象，获取Call对象。
5. 调用Call对象的execute方法，发送HTTP请求并获取Response对象。
6. 从Response对象中获取响应数据，可以是字符串、字节数组、流等形式。
7. 关闭Response对象和OkHttpClient对象，释放资源。
示例代码如下：
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
        .url("http://www.example.com")
        .build();
Call call = client.newCall(request);
Response response = call.execute();
String responseData = response.body().string();
response.close();
client.close();
以上代码发送一个GET请求，请求URL为http://www.example.com，获取响应数据并以字符串形式保存在responseData变量中。注意需要在子线程中执行网络请求，否则会抛出NetworkOnMainThreadException异常。